Stimulation of ANP secretion by 2-Cl-IB-MECA through A 3 receptor and CaMKII

Abstract

Adenosine is a potent mediator of myocardial protection against hypertrophy via A 1 or A 3 receptors that may be partly related to atrial natriuretic peptide (ANP) release. However, little is known about the possible involvement of the A 3 receptor on ANP release. We studied the effects of the A 3 receptor on atrial functions and its modification in hypertrophied atria. A selective A 3 receptor agonist, 2-chloro-N 6-(3-iodobenzyl) adenosine-5′- N-methyluronamide (2-CI-IB-MECA), was perfused into isolated, beating rat atria with and without receptor modifiers. 2-CI-IB-MECA dose-dependently increased the ANP secretion, which was blocked by the A 3 receptor antagonist, but the increased atrial contractility and decreased cAMP levels induced by 30 μM 2-CI-IB-MECA were not affected. The 100 μM 2-(1-hexylnyl)- N-methyladenosine (HEMADO) and N 6-(3-iodobenzyl) adenosine-5′- N-methyluronamide (IB-MECA), A 3 receptor agonist, also stimulated the ANP secretion without positive inotropy. The potency for the stimulation of ANP secretion was 2-CI-IB-MECA ≫ IB-MECA = HEMADO. The inhibition of the ryanodine receptor or calcium/calmodulin-dependent kinase II (CaMKII) attenuated 2-CI-IB-MECA-induced ANP release, positive inotropy, and translocation of extracellular fluid. However, the inhibition of L-type Ca 2+ channels, sarcoplasmic reticulum Ca 2+-reuptake, phospholipase C or inositol 1,4,5-triphosphate receptors did not affect these parameters. 2-CI-IB-MECA decreased cAMP level, which was blocked only with an inhibitor of CaMKII or adenylyl cyclase. These results suggest that 2-CI-IB-MECA increases the ANP secretion mainly via A 3 receptor activation and positive inotropy by intracellular Ca 2+ regulation via the ryanodine receptor and CaMKII.